The title is grammatically correct, albeit possibly confusing. They are their deer = the group owns the group of deer. There, there, dear, it will be all right. (An idiom used to make people feel better, the words "there, there" in this sentence have no particular meaning save for to comfort someone.) There are three separate words: there, their, and they're. "There" shows position, such as, "Over there!" or "I saw three deer there." "Their" shows possession, such as "Their pockets were empty." And "They're" is a contraction of the words "they are" or "they were." "They're delighted feeding them."
"They're very likely to empty their pockets of feed after feeding the deer over there."
Of course, when speaking, no one will know if you are using the appropriate word or not as they all sound similar. (These are called homophones. Words that sound the same but have different meanings and spellings.) When we move to the written word, using the correct word becomes important to know. To know which word to use is not terribly complicated. You can use the following as a guideline:
There - shows position. The word shows where. (Notice how "there" and "where" both have the word "here" in them!?)
Their - shows possession. They own something. It is theirs. Think of the letter "i" as a little stick person, and they own all the letters surrounding them.
They're - a contraction. The apostrophe is your reminder that a word has been shortened and pushed together with another; in this case, the words shortened are "are" or "were." Simple enough to remember, right?
We can move away from "they" and move on to "you"! How is your use of "your" and "you're"? There are only two words to discern this time, and like "their" and "they're," one shows possession, and the other is a contraction! (Yep, you guessed it. The one with the apostrophe is the contraction.) If you are unsure which one to use, place the word "are" into the sentence. For example, if you wanted to text someone, "Your pretty." (You would be grammatically wrong, even if they are pretty.) If you stretch out the sentence, you would say, "You ARE pretty," and know right away you should use "you're." If you text your friend, "It is your turn to drive." You would be correct because if you placed the word "are" in the sentence ("It is you are turn to drive."), you would recognize right away that was incorrect. Therefore the use of "you're" would be wrong.
Since I brought up texting, there is an entirely different vocabulary among the texting community who will shorten words altogether to one or two letters such as "u" and "ur"! An example might be, "u want to go to the party" Notice; there is no capitalization nor punctuation. I understand that texting and tweeting are modes of "compacted communication." I might be inclined to write a book on the proper grammar of "text speech" but for now, you're on your own. I do not find the shortened speak a good substitute for a well-constructed sentence, and I appreciate the time a person has taken to do so. I do not mean to sound like a grammar snob. If the sentence is thought out and written in a longer format, there is less chance of there being any confusion. If you text me, "u free 2nite" I am not clear if you are asking me or telling me. Frankly, I will most likely be making plans with the person who had time to text, "Are you free tonight?"
Love Lots; Smile Often #LLSO